This invention relates to a process for producing coated flat glass in which a metal or metal compound coating is deposited on a face of a freshly formed ribbon of hot glass during its forward travel from a flat glass forming installation to an annealing installation by contacting such face at a coating station with a fluid medium comprising one or more substances from which said coating is formed on said ribbon face.
The coating of glass is extensively practised for conferring desirable radiation absorbing and/or reflecting properties on the product with a view to its use for glazing purposes. Control of the coating step is very important for achieving a coating having those desired properties and which at the same time is of high and uniform optical quality.
It is known that the thickness and quality of the coating formed on the glass ribbon is influenced by the temperature conditions at the coating station or stations. A particularly important influential factor is the temperature of the glass at the position along the ribbon path where it is contacted by the fluid coating material, and the prior art literature contains various proposals for effecting a thermal conditioning of the glass preparatory to deposition of such medium.
Thus for example British patent specification No. GB 2 016 444A (Saint-Gobain Industries) proposes sweeping the ribbon to be coated with a flame in order to bring the glass to an appropriate temperature for the coating operation.
And because the side margins of the glass ribbon leaving the forming installation (for example a float tank) tend to cool more rapidly than the central portion the prior art includes processes wherein the glass is thermally conditioned by heating the ribbon more strongly, or only, at its side margins in order to reduce the temperature gradient across the ribbon prior to coating: see e.g. British patent application No. GB 2 078 710A (BFG Glassgroup) and European patent application No. 0 025 738 Al (Saint-Gobain Vitrage).
In many industrial plants in which coated flat glass is produced, only a proportion of the formed flat glass is coated. Production has to be switched periodically from coated to uncoated glass or vice versa. The switch from one type of product to the other has proved to be quite time consuming. This is because the switch entails adjustments to the annealing installation if the annealing is to proceed in a satisfactory manner. The need for the adjustment of the annealing installation arises because of the cooling effect which is associated with the formation of a coating on the glass ribbon. It has even been found that adjustment to the annealing installation is sometimes required when switching from one type or thickness of coating to another whose formation has a different effect on the temperature of the glass.